The products of olefin oligomerization are usually mixtures of, for example, olefin dimers, trimers, and higher oligomers. Further, each olefin oligomer is itself usually a mixture of isomers, both skeletal and in double bond location. Highly branched isomers are less reactive than linear or lightly branched materials in many of the downstream reactions for which the oligomers are used as feedstocks. This is also true of isomers in which access to the double bond is sterically hindered. In this specification, the olefin types of the oligomers are denominated according to the degree of substitution of the double bond, as follows:
Type I:R—CH═CH2, mono-substitutedType II:R—CH═CH—R, disubstitutedType III:RRC═CH2, disubstitutedType IV:RRC═CHR, trisubstitutedType V:RRC═CRR, tetrasubstitutedwherein R represents an alkyl group, each R being the same or different. Type I compounds are sometimes described as α- or vinyl olefins and Type III as vinylidene olefins. Type IV is sometimes subdivided to provide a Type IVA, in which access to the double bond is less hindered, and Type IVB where it is more hindered.
The degree of branching and double bond Type distribution affect some properties and performance of the olefin derivatives, e.g., the low temperature performance and volatility when converted to alcohols and subsequently to plasticizers.
The degree of branching and mixture of double bond types also affect the reactivity of the oligomer olefins to alkylation and, especially, oxonation. Types I and II have excellent reactivity, Type III fair reactivity, Type IVA good reactivity, and types IVB and V poor reactivity. In alkylation, reactivity is effected by the ease of protonation of the more readily approached, less hindered, double bonds of the preferred structures. Similar effects apply to the reactivity of the oligomer olefins to oxonation, the low branching and less hindered double bonds allowing the molecules to be converted to aldehydes and alcohols rather than being hydrogenated to paraffins.
Furthermore, detergent products obtainable from the products of alkylation of the olefinic oligomer products, especially those having 10 or more carbon atoms, having low Type IVB and V contents and low degrees of branching, would have numerous advantages in use. These include better hard water solubility, and better biodegradability resulting from the lower levels of quaternary carbons.
As examples of the alkylarenes resulting from reaction of oligomer olefins with arenes there may be mentioned the alkyltoluenes, alkylnaphthalenes and, more especially, the alkylbenzenes. Processes for forming these products from arenes and olefins are known per se, and need not be detailed further here. Such alkylarenes are intermediates in the production of advantageous alkylarene sulfonic acids and, after neutralization, of alkylarene sulfonates, also by processes known per se.
There is accordingly a continuing need for olefin oligomerization processes that yield products of a low degree of branching and a low proportion of Type V materials. Advantageously, the products desirably also have, in addition to a low degree of branching, a high proportion of isomers with a single branch which branch is a lower alkyl, i.e., C1 to C3, especially a methyl, branch.
It has been proposed to use as starting materials for oligomerization propylene-rich feedstocks. Such feedstocks tend to yield product with a high proportion of highly branched isomers. Moreover, such feedstocks are becoming increasingly scarce and expensive, and there is therefore also a need to provide oligomerization processes that produce products meeting the above-mentioned requirements from more readily available and less costly feedstocks.
Numerous catalyst systems have been proposed for olefin oligomerization processes. Solid phosphoric acid, nickel- and cobalt-based systems, and acidic crystalline molecular sieves have all been used.